The smile on Diego Costa's face says it all. His regular scowling facial displays expressing his irritations look some distance off what previously was experienced under Jose Mourinho.

Nonetheless, Costa's current form at Chelsea cannot be considered anything less than special, despite his killer-instinct, he remains some distance behind Sergio Aguero regarding ability.

On the contrary, Aguero has role-reversed with Costa by becoming an almost villain character to many for his fraudulent displays this season. Regardless, of what is believed, Aguero maintains his position as the Premier League's most dominant striker.

Just a few short weeks ago Aguero was fighting for his City career, according to reports, but two games later and a world-class performance against Barcelona, Aguero is now a prominent figure at City once again. But that's just typical of Aguero, isn't it? When the going gets tough, the Argentine gets going, and it's usually opposition defences that struggle.

Three managers in twelve months have witnessed a turbulent time in Costa's career. It's only now that Chelsea fans finally see the recapturing of the form he brought after his move from Atletico Madrid in 2014.

What does that speak about Costa? Can he be trusted? Sure, in a match at home to an out-of-form Leicester side, Costa can guide the Blues to victory at home, but with a backlog of fixtures, and the pressure maintaining on his Chelsea side, can he produce? Does he bring the superior performances that Aguero does? No, is the answer.

The fact of the matter is, Aguero has the best minute-to-goal ratio in Premier League history. Along with this, 35% of his goals have come against the 25% of opposition considered City's main rivals. Four goals in eight games against Liverpool. Seven goals in ten games against Chelsea. Four goals in nine games against Arsenal. Eight goals in ten games against Manchester United. Ten goals in ten games against Tottenham Hotspur. 33 goals in 47 games against City's rivals makes scary reading.

Despite this, Costa is the third quickest player to reach 40 Premier League goals, but just three of his goals have come against the same opposition as Aguero has registered 33 against. Yes, Aguero has been in England longer, but he is clearly a player for the big occasion, unlike Costa, who has yet to score against City or Spurs in the league, while just two of his goals have gained Chelsea points against those considered rivals.

Controversy has surrounded Costa's career at Chelsea, his troublesome features overshadowing the frequent displays of brilliance he so often produces for the Blues. Costa's career under Antonio Conte continues to grow from strength to strength, but everyone is awaiting the infamous tantrum regularly generated by the forward when the going gets tough in West London.

Football fans, in particular, suffer from long-term memory loss with the majority of past accomplishments accounting for little or nothing when it comes deciding who truly is better. Costa's achievements of late can only be accredited but until the Spaniard reaches the heights Aguero has over the past half-decade, then only then can the raging bull be considered in the same breath as his Argentine counterpart.

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